Most people worry about the outage itself. Yet for your electronic devices, the most delicate moment is often when the power comes back. Here is what happens at that moment, and why a generator connected to an automatic transfer switch makes the difference.

What happens when the power comes back?

When Hydro-Québec restores a line, the grid is not always stable from the very first second:

  • Voltage spikes can occur as lines are re-energized.
  • Everything restarts at once: heating, refrigerators, pumps, heat pumps and compressors start together and draw a large inrush current.
  • Power can come back and drop again several times while crews carry out repairs and switching.
  • Voltage can be too low for a few moments while the grid settles.

Why it is risky for your devices

Today’s appliances are full of electronics: computers, televisions, appliances with circuit boards, heat pumps, alarm systems, farm or business equipment. A voltage spike or a series of closely spaced outages can damage a circuit board or a power supply. Compressors (refrigeration, air conditioning, heat pumps) also do not like restarting several times in a short period.

With a generator and an automatic transfer switch

The automatic transfer switch (ATS) moves your building from the grid to the generator, then from the generator back to the grid. It is commanded by the generator controller, a Deep Sea DSE6120 on our models. Here is the sequence:

  1. During the outage, your building runs on the generator and is fully separated from the grid. This separation also protects the line workers on the grid.
  2. When the power comes back, your devices do not see it yet: the controller monitors grid voltage and frequency, but the building stays on the generator.
  3. Brief returns are ignored. If the power comes back for a few seconds and drops again, the building does not switch back and forth: it stays on the generator.
  4. The controller waits for the grid to be stable for a return delay set at installation, usually a few minutes.
  5. The transfer then happens in one step, with a short pause between the two sources: never both at once.
  6. The generator keeps running without load for a few minutes to cool down, then stops and returns to standby.

The result: your devices stay on the generator’s stable power during the first, most unstable minutes of the return, and only go back to the grid once it is restored for good.

Stable power during the outage

Our Perkins diesel generators are fitted with a genuine Stamford alternator and an automatic voltage regulator. It keeps the output voltage within about 1%, even as the load changes. Your devices run normally throughout the outage.